This sequence works efficiently if FALLOC_FL_ZERO_RANGE is not supported.
Simple fallocate(0) will extend file with zeroes when appropriate in the
middle of the file if there is a hole there and at the end of the file.
Unfortunately fallocate(0) does not drop the content of the file if
there is a data on this offset. Therefore to make the situation consistent
we should drop the data beforehand. This is done using FALLOC_FL_PUNCH_HOLE
This should increase the performance a bit for not-so-modern kernels or for
filesystems which do not support FALLOC_FL_ZERO_RANGE.
Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Kevin Wolf <kw...@redhat.com>
CC: Stefan Hajnoczi <stefa...@redhat.com>
---
block/raw-posix.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 7866d31..96a8678 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -968,6 +968,23 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData
*aiocb)
#endif
s->has_write_zeroes = false;
+
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+ if (s->has_discard) {
+ int ret;
+ ret = do_fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+ aiocb->aio_offset, aiocb->aio_nbytes);
+ if (ret < 0) {
+ if (ret == -ENOTSUP) {
+ s->has_discard = false;
+ }
+ return ret;
+ }
+ return do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes);
+ }
+#endif
+
+ s->has_discard = false;
return -ENOTSUP;
}
--
1.9.1
